U.S. patent application number 10/586222 was filed with the patent office on 2008-10-09 for process and device for aerobic-thermophilic stabilization and disinfection of sludge.
Invention is credited to Leonhard Fuchs, Martin Fuchs.
Application Number | 20080245729 10/586222 |
Document ID | / |
Family ID | 36657817 |
Filed Date | 2008-10-09 |
United States Patent
Application |
20080245729 |
Kind Code |
A1 |
Fuchs; Leonhard ; et
al. |
October 9, 2008 |
Process and Device for Aerobic-Thermophilic Stabilization and
Disinfection of Sludge
Abstract
A process for the stabilization and disinfection of sludge
wherein a) raw sludge having a dry matter content of from 3 to 7%
by weight is fed continuously or quasi-continuously into a first
stage, where it remains for an average retention time of three to
ten days under aerobic-thermophilic conditions to obtain a
partially stabilized sludge; and b) the partially stabilized sludge
is fed into a second stage in which disinfection of the partially
stabilized sludge is effected at temperatures of at least
50.degree. C., wherein prior to discharging, there is no charging
until the partially stabilized sludge has been disinfected.
Inventors: |
Fuchs; Leonhard; (Mayen,
DE) ; Fuchs; Martin; (Mayen, DE) |
Correspondence
Address: |
OHLANDT, GREELEY, RUGGIERO & PERLE, LLP
ONE LANDMARK SQUARE, 10TH FLOOR
STAMFORD
CT
06901
US
|
Family ID: |
36657817 |
Appl. No.: |
10/586222 |
Filed: |
April 21, 2006 |
PCT Filed: |
April 21, 2006 |
PCT NO: |
PCT/EP2006/061725 |
371 Date: |
October 4, 2006 |
Current U.S.
Class: |
210/603 ;
210/170.06; 210/612 |
Current CPC
Class: |
C02F 2209/44 20130101;
Y02W 10/10 20150501; C02F 2209/22 20130101; C02F 2301/106 20130101;
Y02W 10/15 20150501; C02F 3/006 20130101; C02F 3/121 20130101; C02F
3/26 20130101; C02F 2209/02 20130101; C02F 11/02 20130101; C02F
3/1221 20130101; C02F 2303/04 20130101; Y02W 10/20 20150501; Y02W
10/27 20150501; C02F 2209/04 20130101; C02F 2303/02 20130101 |
Class at
Publication: |
210/603 ;
210/612; 210/170.06 |
International
Class: |
C02F 3/12 20060101
C02F003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 22, 2005 |
DE |
10 2005 018 893.1 |
Claims
1. A process for the stabilization and disinfection of sludge
wherein raw sludge having a dry matter content of from 3 to 7% by
weight is fed continuously or quasi-continuously into a first
stage, where it remains for an average retention time of three to
ten days under aerobic-thermophilic conditions to obtain a
partially stabilized sludge; and said partially stabilized sludge
is fed into a second stage in which disinfection of the partially
stabilized sludge is effected at temperatures of at least
50.degree. C., wherein prior to discharging, there is no charging
until said partially stabilized sludge has been disinfected.
2. The process according to claim 1, wherein said partially
stabilized sludge from the first stage is continuously or
quasi-continuously fed into an intermediate storage tank, from
which it is fed batchwise to the second stage.
3. The process according to claim 1, wherein the average retention
time in the second stage is at least two days.
4. The process according to claim 1, wherein the sludge is agitated
in the first and/or second stages.
5. The process according to claim 1, wherein the time between two
chargings of the first stage is not longer than 12 hours.
6. The process according to claim 1, wherein the time between two
chargings of the first stage is not longer than 6 hours.
7. The process according to claim 1, wherein no charging is
effected for at least four hours.
8. The process according to claim 1, wherein the amount of oxygen
supplied in the first or second stage is controlled depending on
parameters selected from the group of: charged amount of raw
sludge; redox potential in the sludge; oxygen content in the
sludge; oxygen content in the exhaust gas; and CO.sub.2 content in
the exhaust gas.
9. The process according to claim 1, wherein the temperature in the
second stage is within a range of from 50 to 65.degree. C. and is
controlled by supplying or withdrawing heat.
10. The process according to claim 1, wherein the aerobically
stabilized and disinfected sludge is subsequently further treated
physically, chemically and/or biologically.
11. The process according to claim 1, wherein exhaust gas released
in the process is recovered and treated physically, chemically
and/or biologically.
12. A device for the aerobic-thermophilic stabilization and
disinfection of sludge comprising: a raw sludge tank for the
continuous or quasi-continuous charging of raw sludge, which is a
first stage; a disinfection tank for disinfecting the partially
stabilized sewage sludge, which is a second stage; and a conveying
means provided between the raw sludge tank and the disinfection
tank for the batchwise conveying of sludge into the disinfection
tank.
13. The device according to claim 12, further comprising an
intermediate tank provided between the raw sludge tank and the
disinfection tank and connected with both tanks, a first conveyor
for the continuous or quasi-continuous conveying of partially
stabilized sludge from the raw sludge tank into the intermediate
tank, and a second conveyor for conveying sludge from the
intermediate tank into the disinfection tank.
14. The device according to claim 12, comprising at least two
disinfection tanks connected with the raw sludge tank, wherein one
closing means is provided for each disinfection tank, so that at
least one of the disinfection tanks can be closed while at least
one other disinfection tank is open for being continuously or
quasi-continuously filled.
15. The device according to claim 12, wherein said raw sludge tank,
disinfection tank and/or intermediate tank have an agitation device
and/or an aeration device and/or an exhaust device and/or a heat
exchanger.
Description
[0001] The present invention relates to a process and device for
the aerobic-thermophilic stabilization and disinfection of
thickened sludge in several steps.
[0002] A generic process has been described, for example, in
"Korrespondenz Abwasser", 29th year, issue April 1982, pp. 203-207.
In this process, the entering raw sludge, after having been
gravity-thickened, is aerated with simultaneous intense mixing in
two heat-insulated reactors connected in series. In reactor I, the
temperature variation is predominantly around the upper mesophilic
range (30.degree. C..ltoreq.t<42.degree. C.), whereas in reactor
II thermophilic temperatures (.gtoreq.42.degree. C.) are
permanently maintained. With sufficient retention time of each
batch in reactor II and maintenance of the temperatures above
50.degree. C., disinfection is achieved. In this plant, a batch of
stabilized and disinfected sludge is discharged from reactor II
once daily, followed by transferring a corresponding batch from
reactor I to reactor II and finally filling reactor I with raw
sludge. This operation is required to ensure disinfection in
reactor II and has been regular practice to date.
[0003] Drawbacks of this process are the high variations of
temperature, oxygen demand and in some cases pH-value in reactor I
and the temporarily occurring odor emissions, since 30 to 50% of
the reactor contents are usually replaced by raw sludge at once
when the tank (reactor) is charged. For larger plants with three
tanks, these problems can even aggravate.
[0004] DE-PS 28 52 544 discloses a process for the stabilization
and large disinfection of sewage sludge obtained from waste water
treatment plants in a temperature range of above 40.degree. C., in
which the sewage sludge is charged into an arrangement of one or
more heat-insulated tanks, circulated by a controlled supply with
atmospheric oxygen and thereby degraded exothermally. The process
was characterized in that the supply with atmospheric oxygen should
be feedback-controlled to maintain an almost constant sludge
temperature. This process was unsuitable since the degradation of
cold sludge cannot be accelerated significantly by increasing the
supply with atmospheric oxygen. Reduction of the supply with
atmospheric oxygen at high temperatures in the sludge leads to an
unsatisfactory stabilization.
[0005] DE-AS-28 52 545 discloses a process for the stabilization
and large disinfection of sewage sludge obtained from waste water
treatment plants in a temperature range of above 40.degree. C., in
which the sewage sludge is fed into an arrangement of one or more
heat-insulated tanks, circulated by a controlled supply with
atmospheric oxygen and thereby degraded exothermally. The process
was supposed to be characterized in that the filling volume of the
tank arrangement would be varied if the feed or the composition of
the sewage sludge varied. Thus, it should be achieved that the
average retention time of the sewage sludge in the tanks is almost
constant irrespective of the feed. This process could not eliminate
the difficulties either which arise from the high peak loads in the
discontinuous feeding of the first stage of multiple-stage plants
for the aerobic-thermophilic stabilization and disinfection of
sewage sludge.
[0006] Therefore, it is the object of the invention to develop a
process and a device for the stabilization and disinfection of
sludge which overcome the drawbacks of the prior art.
[0007] This object is achieved by a process for the stabilization
and disinfection of sludge wherein [0008] a) raw sludge having a
dry matter content of from 3 to 7% by weight is fed continuously or
quasi-continuously into a first stage, where it remains for an
average retention time of three to ten days under
aerobic-thermophilic conditions to obtain a partially stabilized
sludge; [0009] b) said partially stabilized sludge is fed into a
second stage in which disinfection of the partially stabilized
sludge is effected at temperatures of at least 50.degree. C.,
wherein prior to discharge, there is no charging until said
partially stabilized sludge has been disinfected.
[0010] In contrast to the prior art, the raw sludge is fed
continuously or quasi-continuously, so that the composition does
not change in the first stage, or only slightly so. This avoids the
disadvantageously high variations of parameters such as
temperature, oxygen demand or pH-value and reduces odor emissions,
in particular.
[0011] In the disinfection step, a continuous or quasi-continuous
operation is not possible since a minimum retention time, resp.
minimum isolated reaction time for disinfection must be ensured.
The necessary time (minimum time) for disinfection of the sludge
depends on the temperature in the second stage. According to the
second working report of the ATV/VKS Working Group "Entseuchung von
Klarschlamm" in "Korrespondenz Abwasser", Volume 35, Issue January
1988, pages 71 to 74, a minimum time of 23 hours is required at
temperatures of 50.degree. C., a minimum time of 10 hours is
required at temperatures of 55.degree. C., and a minimum time of
four hours is required at temperatures of 60.degree. C. These
minimum times as a function of the temperatures are to be observed
as lower limits. According to a working paper of the European Union
on the topic "Sludges" (third draft) of Apr. 27, 2000, a minimum
time of 20 hours at a temperature of at least 55.degree. C. is
demanded for disinfection. These data are consistent with the
values demanded by the American Environmental Protection Agency.
Corresponding minimum times for disinfection are preferred. With
continuous feeding, disinfection would not be possible. The
respective newly fed, non-disinfected sludge would re-inoculate the
sludge.
[0012] In the first stage, at least partial stabilization of the
sludge is achieved. The stabilization and disinfection are then
completed in the second stage, also in the thermophilic range.
[0013] A sludge is considered stabilized if it can be stored for an
extended period of time or be used on agricultural land without
problems. This condition is typically achieved if the organic
content is reduced by about 30 to 50%, preferably more than 40%.
The organic content is determined by the loss on ignition of a
dried sample according to DIN 38409.
[0014] While in the prior art the temperatures in the first tank
usually vary about the upper mesophilic range, temperatures in the
thermophilic range, i.e., of at least 42.degree. C., are reached in
the first stage according to the invention. Preferably, the
temperatures in this stage are at least 45.degree. C., more
preferably at least 48.degree. C. and most preferably above
50.degree. C.
[0015] In a particularly preferred embodiment, the sludge is fed
continuously into the first stage. However, the feeding may also be
effected intermittently. Preferably, raw sludge is fed at least
once per hour. At least, the sludge should be fed more frequently
than every 20 hours, more preferably at least every 12 hours, and
even more preferably at least every 6 hours. The time intervals
depend on the amount of raw sludge obtained and the necessary
retention times in the first stage to achieve the intended partial
stabilization. For example, if the average retention time in the
first stage is five days and feeding is effected at intervals of 6
hours, only one 20th, i.e., 5% of the total contents, must be
exchanged each time, so that disturbing variations in the
composition in the first stage are substantially avoided.
[0016] Apart from regular feeding, it is also possible to couple
feeding to working times, for example, to feed the plant hourly or
two-hourly during the working time between 7 a.m. and 8 p.m. and
not to perform feeding between 8 p.m. and 7 a.m. hours.
[0017] The stages are preferably agitated to achieve mixing of
newly added raw sludge with already partially treated sludge. In
addition, an oxygen-containing gas is typically introduced at least
in the first stage. As in the prior art plants, the aeration
intensity, aeration time and/or oxygen content of the gas supplied
is controlled. Typical measured and controlled quantities for the
oxygen supply are the amount of raw sludge, the redox potential or
oxygen content in the sludge, and the oxygen content or CO.sub.2
content of the exhaust gas.
[0018] Typically, the retention time in the first stage is three to
ten days, more preferably four to seven days. In the second stage,
the retention times are typically from one to three days.
[0019] It is required that the temperature for disinfection in the
second stage is within a range of from 50 to 65.degree. C.,
preferably from 55 to 60.degree. C. This may be controlled by
heating or cooling. The heat withdrawn may be used for heating
nearby buildings, for example.
[0020] The process is performed in several heat-insulated,
preferably mixed tanks with supply of oxygen-containing gas, it is
safe and uniform, stabilizes well and disinfects perfectly, avoids
offensive smells and is comparable with previous processes with
respect to costs.
[0021] In accordance with this application, a tank is any suitable
container, i.e. a basin. Such tanks are also referred to as
reactors.
[0022] The invention also relates to a device for the
aerobic-thermophilic stabilization and disinfection of sludge.
[0023] The device according to the invention has a raw sludge tank
for the continuous and/or quasi-continuous feeding of raw sludge,
which constitutes a first stage. Further, the device has a
disinfection tank for disinfecting the sewage sludge partially
stabilized in the first stage, which forms a second stage. Between
the two tanks, there is a conveying means, which comprises pumps
and valves, in particular, for the batchwise conveying of sewage
sludge from the raw sludge tank into the disinfection tank. The
device according to the invention is suitable, in particular, for
performing the above described process.
[0024] A preferred embodiment of the device according to the
invention has an intermediate tank between the raw sludge tank and
the disinfection tank. The intermediate tank is connected with both
the raw sludge tank and the disinfection tank. In this preferred
embodiment, the conveying means is divided in two, so that a first
conveying means is provided between the raw sludge tank and the
intermediate tank for the (quasi-)continuous conveying of raw
sludge into the intermediate tank, and a second conveying means is
provided between the intermediate tank and the disinfection tank
for the batchwise conveying of sewage sludge.
[0025] The providing of at least one intermediate tank has the
advantage that the contents in the raw sludge tank are subjected to
small variations only.
[0026] In a further preferred embodiment of the invention, at least
two disinfection tanks are provided in addition to the raw sludge
tank which constitutes the first stage. The disinfection tanks are
in turn connected with the raw sludge tank. In the connection,
especially a pipeline system, a conveying means is again provided.
In this embodiment, one closing means is provided for each
disinfection tank. Thus, it is possible to close one disinfection
tank and open the other. Then, sewage sludge is continuously or
quasi-continuously transferred from the raw sludge tank into the
opened disinfection tank. As soon as one disinfection tank is
completely filled, it is closed, and sewage sludge is continuously
or quasi-continuously conveyed from the raw sludge tank into the
second or a further disinfection tank.
[0027] It is also possible that several tanks are used in one or
more of the stages, and less tanks in other stages. In this case,
the tank sizes are to be chosen to match the desired procedure. For
example, there may be two first tanks, from which the sludge is
transferred, for example, into an intermediate tank from which the
sludge is then transferred into a disinfection tank.
[0028] In the following, the invention is further illustrated by
means of preferred embodiments with reference to the drawings
wherein:
[0029] FIG. 1 shows a schematic view of a first preferred
embodiment of the device according to the invention;
[0030] FIG. 2 shows a schematic view of a second preferred
embodiment of the device according to the invention;
[0031] FIG. 3 shows a schematic view of a third preferred
embodiment of the device according to the invention.
[0032] FIG. 1 shows a particularly simple type of design. The raw
sludge tank 1 with stage 1 is fed continuously or
quasi-continuously. The raw sludge tank 1 is filled thereby between
minimum and maximum levels. Via the aeration device 12,
oxygen-containing gas is supplied, and exhaust gas is removed via
an exhaust device 13. In stage 1, mixing may also be effected by
means of agitation device 11. Heating or cooling is achieved by
heat-exchanger 10.
[0033] From stage 1, partially stabilized sludge is transferred
into a disinfection tank 2 with stage 2, in which a heat exchanger
10, an agitation device 11, an aeration device 12 and an exhaust
device 13 may also be provided. Due to the discharge from stage 1
effected by the conveying means 15, the sludge level in the raw
sludge tank 1 decreases to the minimum value again. In stage 2,
disinfection is then performed during the minimum isolated reaction
time. Subsequently, part of the material is discharged from stage 2
and transferred to further processing.
[0034] In larger plants, it is appropriate to provide an
intermediate tank or intermediate storage tank Z as represented in
FIG. 2. Raw sludge is continuously or quasi-continuously fed in
stage 1 to achieve partial stabilization. In this stage, a heat
exchanger 10, an agitation device 11, an aeration device 12 and an
exhaust device 13 may be provided. Discharge of partially
stabilized sludge by a first conveying means 16 and transfer to the
intermediate storage tank Z is effected continuously or
quasi-continuously depending on the feed. Due to the continuous or
quasi-continuous discharge from stage 1, the intermediate storage
tank Z is gradually filled. The intermediate storage tank Z may
also include a heat exchanger 10, an agitation device 11, an
aeration device 12 and an exhaust device 13.
[0035] Transfer from the intermediate storage tank Z into the
disinfection tank 2 with stage 2, which functions as described
above for FIG. 1, is then performed batchwise by a second conveying
means 17.
[0036] It is advantageous that the feeding of stage 1 may be
performed continuously without essential variations to the filling
level. The average retention time in the intermediate storage tank
Z is preferably 0.5 to 1.5 days.
[0037] The conveying means 16 may be a valve, so that gravity is
used for conveying. In addition to the valve, a pump may be
provided, wherein a valve is preferably inserted accordingly
upstream and downstream from the pump second conveying means
17.
[0038] A particularly preferred embodiment is shown in FIG. 3. In
this case too, stage 1 is fed continuously or quasi-continuously as
described above. What may be provided is a heat exchanger 10, an
agitation device 11, an aeration device 12 and an exhaust device
13. This is followed by two stages 2 and 2' which are operated
alternately as intermediate storage tank and disinfection tank. At
first, partially stabilized sludge from stage 1 is transferred with
a conveying means 18, upstream from which a valve (not shown) may
be inserted, into the disinfection tank 2, which may optionally
have a heat exchanger 10, an agitation device 11, an aeration
device 12 and an exhaust device 13. The feeding of this tank is
also effected continuously or quasi-continuously. After this tank
has reached a maximum filling level, the disinfection tank 2 is
closed by closing means 19 and not filled further, and the
continuously discharged sludge from stage 1 is transferred into the
disinfection tank 2'. Thus, the closing means 20 is opened. The
disinfection tank 2' may also have a heat exchanger 10, an
agitation device 11, an aeration device 12 and an exhaust device
13.
[0039] Disinfection now takes place in disinfection tank 2, i.e.,
no further charging is performed during the minimum isolated
reaction time. Subsequently, the disinfected sludge is wholly or
partially discharged from the disinfection tank 2. During this
time, the disinfection tank 2' is filled continuously or
quasi-continuously. After the disinfected sludge has been
discharged from the disinfection tank 2, the sludge discharged from
stage 1 is again transferred into disinfection tank 2, and
disinfection is effected in disinfection tank 2'.
[0040] Instead of an agitation device 11 and an aeration device 12,
a device which combines the functions of agitation and aeration or
aeration, agitation and foam-control in itself may also be
provided.
[0041] The heat exchangers in the different stages serve for
increasing or decreasing temperatures in individual stages in order
to obtain the desired process values.
[0042] Depending on the kind of sludge and its content of
aerobic-thermophilically degradable organic matter, the average
retention time in the whole plant is between five and twelve days,
and in a range of seven to nine days for usual municipal sewage
sludges.
[0043] The process according to the invention is for the treatment
of thickened sludge as obtained from the mechanical and/or
biological treatment of domestic and/or industrial sewage, in
particular, and a dray matter content (DS) of from 3 to 7%,
preferably from 4 to 6%, is achieved by gravity or mechanically.
Such thickened sewage sludges generally contain sufficient organic
matter for the exothermic aerobic-thermophilic degradation in stage
1.
[0044] Their Theological properties are such that they are easy to
handle. Especially, if a preheating of the thickened raw sludge or
a heating of stage A is to be avoided, a dry matter content (DS) of
the raw sludge of about 4 to 5% is recommendable. Then, within the
predetermined retention time of preferably four to eight days,
enough heat is released in the first stage to reach the desired
thermophilic temperatures autothermally.
[0045] The supply of oxygen may be controlled by the aeration
intensity, aeration time and/or oxygen content of the gas supplied.
The controlling is optionally effected in accordance with the
content of aerobic-thermophilically degradable organic matter, the
redox potential or oxygen content in the sludge, and the oxygen
content or CO.sub.2 content in the exhaust gas.
[0046] Useful tanks include all agitated and aerated reactors as
used in waste water and sludge technology, which may preferably be
equipped with means for foam control. The supply and withdrawal of
heat is effected by usual heat exchangers. Undesirable heat losses
are avoided by a sufficient insulation of the tanks.
[0047] The process according to the invention may be applied not
only to the aerobic-thermophilic stabilization and disinfection of
sewage sludge, but also to liquid manure and other organic
concentrates, such as waste from yeast production and food wastes.
It has been found that the process according to the invention
stabilizes reliably and well and disinfects safely without causing
offensive smells. A biological further treatment in the mesophilic
temperature range, i.e., at about 20 to 40.degree. C., is
possible.
[0048] Exhaust gas released from the process may also be recovered
and treated physically, chemically and/or biologically.
[0049] The aerobic-thermophilically stabilized and disinfected
sewage sludge is preferably used in liquid form on agricultural
land. Of course, humification or dewatering is also possible.
* * * * *